The detection of exoplanet Kepler-37b demonstrates that sun-like stars in our galaxy are able of hosting much smaller planets than anything seen before in our solar system.

Image: NASA/Ames /JPL-Caltech/

The detection of a tiny planet has shown for the first time that stars in our galaxy are able to host much smaller planets than anything seen in our own solar system.

The existence of the planet, Kepler-37b, the innermost of three planets that orbit the sun-like host star, Kepler-37, is announced in the journal Nature.

The University of Sydney's Professor Tim Bedding, Head of the School of Physics, and Dr Dennis Stello, an Australian Research Fellow in the School, contributed to the discovery effort of an international team.

"That we have found one of these small and hard-to-detect planets suggests that they are abundant around other stars and lends weight to the belief that as planet size decreases their occurrence increases exponentially," said Dr Stello.

Kepler-37b is an exoplanet, or planet located outside the solar system, and is estimated to be a similar size to Earth's moon, which is only 3475 kilometres in diameter.

Owing to this extremely small size and its highly irradiated surface, Kepler-37b is believed to be a rocky planet with no atmosphere or water, similar to Mercury.

The Kepler spacecraft made the Kepler-37b finding possible. The spacecraft was launched in 2009 with the goal of determining how often rocky planets occur in the habitable zone around sun-like host stars in our galaxy.

Over 150,000 stars are continuously monitored for transits of planetary bodies. Over the course of 978 days of observations by the Kepler spacecraft, transit signals of three planets of the star Kepler-37, a slightly cooler and older star than our sun, were identified.

"While theoretically such small planets are expected, detection of tiny planet Kepler-37b is remarkable given its transit signal is detectable on less than 0.5 percent of stars observed by Kepler," Professor Bedding said.

"Since the discovery of the first exoplanet we have known that other planetary systems can look quite unlike our own, but it is only now, thanks to the precision of the Kepler space telescope that we have been able to find planets smaller than the ones we see in our own solar system."

Professor Bedding and Dr Stello contributed to the analysis of Kepler-37, the star Kepler-37b orbits.

"We analysed the frequencies of standing sound waves inside the star to tell its size in the same way that you could tell the difference in size of a violin and cello by the difference in the pitch of the sound they produce," said Dr Stello.

This asteroseismic analysis showed that the radius of Kepler-37 is about 20 percent smaller than the sun.

"Knowing this stellar radius is very important because the accuracy with which we can measure the radius of the planet Kepler-37b is limited by how accurately we can calculate the radius of Kepler-37," said Dr Stello.

"Our work from here is to keep working with the planet team at NASA to make seismic analyses of planet-hosting stars, and there are some exciting results in the pipeline," said Dr Stello.